This invention generally relates to signal processing systems and, more particularly, to improving the accuracy and reliability of such a system which uses a velocity detector in the form of a microwave transceiver and which takes advantage of the Doppler effect to obtain an electrical velocity information signal.
The application of microwave transceivers which use the Doppler effect to determine velocity are well known. Such applications include, for example, vehicular speed detection employed by police officers to enforce highway speed limits and equipment such as farm implements wherein it is desirable to determine not only the velocity of the implement but also the distance or acreage that it has covered. By obtaining a precise velocity measurement, accurate distance and acreage measurements may be derived by conventional techniques.
With respect to farm implements, transceiver systems are particularly useful because they tend to be more accurate than conventional mechanically-driven systems because wheel slippage is not a factor.
In addition, it is desirable in such systems to increase the signal-to-noise ratio and minimize the effects on accuracy resulting from environmental variations such as temperature, humidity or the like. Many such systems do not involve any RF amplification; hence, merely increasing the gain of the antenna or other parts of the system has not yielded a practical improvement in the signal quality. Using a microwave transceiver with a circulator and mixer, which in essence is a superheterodyne system, results in some improvement and with which the present invention may be used to obtain greater improvement. Another desirable feature is to provide a system which does not produce spurious information signals when the actual velocity of the vehicle on which the system is mounted is zero. Such spurious signals may be generated even though the vehicle has stopped because of the system responding to vehicle vibrations, rustling leaves, blowing dirt, or the like. Moreover, it is desirable to provide a means for manually or automatically suspending operation of the system when the vehicle is traversing areas which are not to be included in the measurement, such as roads, bridges or the distance between different areas to be measured or when the implement for which the measurement is being made (e.g. a sprayer) is deactivated.
Reference may be had to one particular such system disclosed in U.S. Pat. No. 3,895,384 which is assigned to the assignee of the present invention. Although the system disclosed therein offers significant advantages over the prior art, the system of the present invention has additional desirable attributes and features that result in improved operational performance and expanded functional capabilities.